Interpolate between trackpoints (interpolate)

This filter modifies any tracks so that either the distance or the time
between consecutive points is no less than the specified interval. Where
points are missing, the filter fills them in by following a straight
line (actually a great circle) between the adjacent points. You
must specify either the
distance or the time option.

Example 4.5. Using the interpolate filter

This command line reads track.gpx and inserts points wherever two adjacent
trackpoints are more than 10 seconds apart: